*3.1.2. Use of local strains of viruses*

vaccination may result in vaccine failure in poultry flocks. The fault of administering the

If the optimum dose of vaccine had not been injected in the bird, then there is also failure of vaccine. Overdosage may lead to reaction, and underdosage can lead to vaccine failure. There are certain factors which cause reduction in optimal vaccine dosage, that is, use of chlorinated water for vaccination, use of water having antimicrobial contents, etc. Moreover, in the case of injecting vaccine to more number of birds than recommended by the company or manufacturer, the low dose will be available to the whole the flock and thus may be prone to low

Some of the vaccines require a booster dose for successful immunization. The booster dose is required after 10–20 days of the initial dose. The initial dose is required for priming of vaccine while the booster is required for maximum protection against antigen. The lack of booster

Mostly the vaccines should be done early in the morning or later if it is during summer. The birds feel comfortable during cold hours of the day. As a result, a good response is obtained after vaccination. Otherwise, the chances of vaccine failures are increased in the case of vac-

The climate variation is a change in climatic parameters (temperature, rainfall, humidity and soil moisture) [23]. Climate change affects both living and nonliving creatures, thus contributing to the health of poultry flocks and may lead to vaccine failure and disease

The following procedures can prevent vaccine failure in livestock and poultry flocks.

The vaccines must be properly formulated. The dosage of vaccinal antigen and properly processed vaccines provide good results and prevent vaccine failure. The record of all batches of

dose results in low antibody titers, resulting in vaccine failure.

vaccine also results in vaccine failure [3, 4].

84 Immunization - Vaccine Adjuvant Delivery System and Strategies

*2.2.7. Inadequate dosage*

vaccine titers and vaccine failure.

*2.2.9. Wrong timing of vaccination*

**3. Preventing vaccine failure**

*3.1.1. Proper formulation of vaccine*

cinating birds during the hot hours of the day.

*2.2.8. Lack of booster dose*

*2.2.10. Climatic factors*

**3.1. Vaccine factors**

outbreaks.

For maximum immune protection, the local strains of antigens must be used for manufacturing of vaccine. The local disease causing agents of any area are specific targeted pathogens and antigens from local disease outbreaks and provide maximum protection against local disease causing organisms.
